Abstract
To achieve high power conversion efficiencies in photovoltaic or photoelectrochemical cells, an understanding of the dynamical processes in the electrode materials upon photoexcitation is crucial. Antimony sulfide is a promising candidate material. The authors present time-resolved two-photon photoemission measurements from a Sb${}_{2}$S${}_{3}$(100) single crystal surface. A first laser pulse generates a population of free charge carriers that are probed by a second pulse. Ultrafast relaxation towards the conduction band minimum is followed by a fast decay within 1.3 ps into two longer-lived trap states, self-trapped electrons and self-trapped excitons states, with lifetimes of 27 and 63 ps, respectively. The results support a polaronic self-trapping mechanism by optical phonons.
Highlights
The conversion of solar energy in high-efficiency lowcost photovoltaic or photoelectrochemical solar cells that can be built from stable, abundant, and nontoxic materials is a desirable approach for a sustainable energy production at the large scale
The valence band (VB) onset was determined by linear extrapolation of the falling edge as EVBM − EF = (−1.06 ± 0.10) eV, in good agreement with the value recently published in Ref. [5] based on x-ray photoelectron spectroscopy (XPS) measurements
Energetically high-lying conduction band states (CBS) are populated by absorption of pump photons
Summary
The conversion of solar energy in high-efficiency lowcost photovoltaic or photoelectrochemical solar cells that can be built from stable, abundant, and nontoxic materials is a desirable approach for a sustainable energy production at the large scale. When investigating suitable low-cost systems that deliver high PCE, interest in antimony-based chalcogenides like antimony sulfide (Sb2S3) or antimony selenide (Sb2Se3) arose. Both materials show a high stability, consist of earthabundant elements, and can be synthesized at comparatively low temperatures. The crystal structure is strongly anisotropic with covalently bonded one-dimensional (1D) ribbons that are in turn bonded to each other by much weaker van der Waals forces [1,2]. Owing to this ribbon structure the bonds at the grain boundaries are saturated which reduces recombination losses [3].
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